Infectious diseases remain a leading cause of illness and death worldwide, particularly among children. However, there exist today relatively few physicians dedicated to investigating fundamental scientific questions relating to infections in children. The Division of Pediatric Infectious Diseases at Yale University is a diverse group of academic basic scientists and clinical researchers who have made important contributions to our understanding of both the pathogenesis and epidemiology of infections in children. For over 20 years, this division has trained highly motivated pediatricians for a productive career in infectious diseases research. The success of this program is best measured by the accomplishments of our former trainees, many of whom have assumed major leadership roles in academic centers, government agencies, and industry. Support from the NIH is requested in order to train two individuals per year for the next five years. Individuals will be recruited into the fellowship following completion of pediatric residency training. The three year fellowship period will consist of one year of clinical training at the Children's Hospital at Yale-New Haven, which will involve inpatient and outpatient management of infectious diseases. This clinical experience will be complemented by two additional years of closely mentored and intensive training in basic sciences or clinical research. Formal didactic teaching will be available through courses offered by Yale graduate school departments, including Epidemiology and Public Health, Microbiology, Immunology, Cell Biology, Genetics, and the Clinical Scholars Program. Fellows may choose one of two research tracks designed to highlight the unique expertise and training capabilities of the Yale faculty mentors. Those who select the Pathogenesis of Infectious Diseases track will have the opportunity to study molecular mechanisms underlying the pathogenesis of infectious diseases caused by viruses, bacteria, fungi, parasitic protozoa and helminths. Those choosing the Epidemiology of Infectious Diseases track will develop expertise in such areas as perinatal HIV transmission, hospital infection control, the natural history of lyme borreliosis, studies of vaccine efficacy, molecular epidemiology, and infections in special hosts. Fellows will also receive mentoring in career development, ultimately facilitating the transition from fellow to independent investigator. It is a goal of this program to assist in addressing the pressing need for highly trained clinical and basic science investigators in Pediatric Infectious Disease.